A condition in which there are not enough healthy red blood cells to deliver adequate oxygen to the body, usually measured by a decrease in the amount of hemoglobin. Hemoglobin Illustration: linkhere Some symptoms include weakness, pale skin, rapid heartbeat, shortness of breath, dizziness, headache, numbness or coldness in extremities. There are several causes of anemia such as vitamin deficiency and kidney failure to name a few. Certain chronic diseases such as cancer can also cause anemia by interfering with the production of red blood cells. A hormone called erythropoietin, which is produced by the kidneys, stimulates bone marrow to produce red blood cells. With GIST, a shortage of this important hormone can be a side effect of chemotherapy such as Gleevec or Sutent. Treatment with injections of drugs such as Procrit or Aranesp can stimulate the bone marrow to produce the needed red blood cells.